The use of printing technology is of great interest in the various areas ranging from thin film transistors (TFTs), energy storage devices, solar cells to micro electro-mechanical system (MEMS). In this wide variety of applications, preparations of various inks comprising semiconductors, biological materials, carbon, and conductive oxides have been reported.
One exemplary potential candidate for use as ink in such printing technology in view of its abundance, high theoretical capacity and environmental compatibility is manganese dioxide (MnO2).
MnO2 is usually regarded as an ideal candidate for the electrode materials of portable devices, water treatment, up-conversion as well as photocatalysis.
Conventional MnO2 electrodes are mainly prepared by two approaches:    (1) nanostructured MnO2 or MnO2-containing composite precipitates via a wet chemical process.
In this process, precursors are typically enclosed in a stainless steel autoclave at round 85° C. for 24 h. A flexible and free-standing composite paper could be prepared with high MnO2 mass loading (Sumboja, et al., Adv. Mater., 25(20): 2809-2815 (2013)). This composite paper can serve as the electrode materials for the supercapacitor and achieve an areal capacitance of 897 mF·cm−2.    (2) direct electrodeposition or chemical deposition on various substrates (e.g. glass, quartz, copper or aluminum foil).
For example, MnO2 has been electrodeposited on the surface of graphene to improve the conductivity of the electrode (Yu, et al., Nano Lett., 11(10): 4438-4442 (2011)).
However, these existing preparation methods for MnO2 are relatively high cost, involve complicated processes and tend to include superfluous contamination from the preparation process.
Binders may also sometimes be added to increase the rigidity during the coating process. For example, a cathode composite ink comprised of electrolytic MnO2, graphite and binder (polyvinylpyrrolidone (PVP), polytetrafluoroethylene (PTFE) or polyethylene oxide (PEO)) as described in US Published Application No. 2011/0274959. However, it is known in the art that the introduction of insulating binders would cause agglomeration in the inks, leading to the reduction of electrical conductivity and instability of the ink.
Accordingly, the goal of developing environmentally-benign and binder free MnO2 ink remains unaddressed, which has prevented adoption of high-efficiency and large-scale printable processes using inks comprising MnO2. Furthermore, due to an ever increasing demand for miniature and low cost power sources, there exists an ongoing need for a method of preparing MnO2 ink with increased efficiency and yield.
There also exists a need for MnO2 ink based energy storage devices with improved electrochemical properties, which may provide sufficient power to drive a device, such as a wearable device, LEDs and LCD clock(s).
Therefore, it is an object of the disclosure to provide an improved method of preparing concentrated MnO2 ink addressing at least one or more of the above deficiencies, that would allow the synthesis of aqueous MnO2 ink more efficiently and at a lower production cost.
It is a further object of the disclosure to provide a device having one or more MnO2 components, together with an electrolyte of ionic liquid.
It is a further object of the disclosure to provide an interdigital transparent SC (IT-SC) device comprising aqueous MnO2 ink.